GUI: Widgets to implement loaders or port to EML

[sppmacd]

• ArrowButton
• Border
• Button - finish theme overrides
• Canvas
• Checkbox
• ColorPicker
• ColorPickerDialog - port to EML
• Console
• Layout: Support direction property
• Datebox
• FileExplorer - port to EML
• FilePrompt - port to EML
• Frame
• Grid
• Listbox
• ListView
• MessageBox (only instantation/register)
• Overlay (handle ID)
• Progressbar
• Prompt (only instantation/register)
• RadioGroup
• SelectWidget (this is a template, may be hard)
• SettingsMenu
• Slider (mode, exponent, wraparound)
• StateTextButton (a template)
• TabWidget (preselected_tab)
• TextButton (font_size, alignment)
• Textfield (alignment)
• ToolWindow (position)
• Widget (enabled, visible, background_color)
• WidgetTreeRoot (handle ID)
• sprites/RectangleShape
• sprites/Sprite